Here is an old guide https://www.reddit.com/r/Bitcoin/comments/7lu6ze/an_extensive_guide_for_cashing_out_bitcoin_and/
I have had some insight into cashing out through bitstamp and what questions they ask once you have a bit higher amounts to get to your bank. For now they don't have a limit.
My plan would be:
1. Have an account at Swissquote. They will soon accept Crypto deposits. They already cold store (so the say) crypto you bought through them. Their partner exchange is Bitstamp btw.
2. CSC to BTC on NLexch.
3. BTC to Nano S
4. Call Swissquote and request a meeting. I live in Switzerland, so that's why I can do that easily.
5. Rent security detail for a day and show up at their offices, together with my tax adviser, set up a contract on how they will handle the transaction and specify their one and only role, which is to trade btc to fiat and then send it to my private bank account. Execute the transfer from my Nano S to their specifically for me created address and then slowly, over the day, execute the trade in constant check with the order book.
6. In advance contact my bank advisor and let them know about a big transaction hitting my account soon. Provide ALL documentation about any trade I have made and any deposit that has gone from them to Bitstamp. Collaborate to a maximum.
Points in my favour, and not transferable
a) Swissquote and I have the same jurisdiction, I have already spoken to them.
b) I have the best tax adviser one can wish for
c) I know the guys personally at my bank, because I did my apprenticeship there. I understand their compliance procedures and I can escalate to the branch manager. We go by first name with each other.
d) I can have connections to trustworthy security detail. If this fails, I can just go there myself, still armed. Or bring some friends along.
e) I have collected all trade and fiat-to-exchange data and all source of funds is documented.
In any case: The critical points are:
1. the csc to btc or fiat trade. Wathc the order book, to not fuck it up and get a horrible average price
2. exchange to bank account
3. cash hits your bank account. "Sir, please explain where USD 15mio come from, when you poor son of a gun only make $1800 per month"
4. Tax matters
Finally: You must be an idiot to keep the cash at your bank. It needs to be invested. And here a totally new journey starts. Happy to write about that. I have done so at xrpchat, but it never turns out to be a healthy debate.